U.S. patent number 7,832,613 [Application Number 12/354,221] was granted by the patent office on 2010-11-16 for friction stir welding system.
This patent grant is currently assigned to General Electric Company. Invention is credited to Timothy Hanlon, Earl Claude Helder, Pazhayannur Ramanathan Subramanian, Timothy Joseph Trapp.
United States Patent |
7,832,613 |
Hanlon , et al. |
November 16, 2010 |
Friction stir welding system
Abstract
A system, in certain embodiments, includes a backing plate, a
tungsten-based member disposed along the backing plate, wherein the
tungsten-based member defines a welding work surface, and the
tungsten-based member comprises curved grooves configured to secure
the tungsten-based member to the backing plate. The system also
includes a drive. The system includes a pin tool movable by the
drive to create friction along one or more workpieces disposed on
the welding work surface, wherein the frictional heating and
mechanical stirring is configured to create a stir weld along the
one or more workpieces. The system, in some embodiments, also may
include a backing plate comprising liquid passages and gas passages
and a tungsten-based member disposed along the backing plate,
wherein the tungsten-based member defines a welding work
surface.
Inventors: |
Hanlon; Timothy (Glenmont,
NY), Trapp; Timothy Joseph (Wyoming, OH), Helder; Earl
Claude (Cincinnati, OH), Subramanian; Pazhayannur
Ramanathan (Niskayuna, NY) |
Assignee: |
General Electric Company
(Niskayuna, NY)
|
Family
ID: |
42106274 |
Appl.
No.: |
12/354,221 |
Filed: |
January 15, 2009 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20100176182 A1 |
Jul 15, 2010 |
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Current U.S.
Class: |
228/2.1;
228/112.1 |
Current CPC
Class: |
B23K
37/06 (20130101); B23K 20/126 (20130101); B23K
20/1245 (20130101) |
Current International
Class: |
B23K
20/12 (20060101); B23K 37/04 (20060101) |
Field of
Search: |
;228/2.1,112.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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151020 |
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Dec 2004 |
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EP |
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9253890 |
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Sep 1997 |
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JP |
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WO02100586 |
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Dec 2002 |
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WO |
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Other References
US. Appl. No. 11/554,751, filed Oct. 31, 2006, Applicant:
Subramanian; Entitled: "Method for Controlling Microstructure via
Thermally Managed Solid State Joining". cited by other .
European Search Report dated May 20, 2010. cited by other.
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Primary Examiner: Ward; Jessica L
Assistant Examiner: Patel; Devang R
Attorney, Agent or Firm: DeCristofaro; Richard A.
Claims
The invention claimed is:
1. A stir welding system, comprising: a backing plate, comprising a
cavity; a tungsten-based member disposed along the backing plate
and received by the cavity, wherein the tungsten-based member
defines a welding work surface and the tungsten-based member
comprises curved grooves configured to secure the tungsten-based
member to the backing plate, such that the member and backing plate
define generally flush welding work surface including both the
backing plate and the member; a drive; and a pin tool movable by
the drive to create friction along one or more workpieces disposed
on the welding work surface, wherein the frictional heating and
mechanical stirring is configured to create a stir weld along the
one or more workpieces.
2. The stir welding system of claim 1, wherein the tungsten-based
member comprises an arcuate surface opposite from the welding work
surface, wherein the welding work surface is generally flat and
wherein the curved grooves are recessed in the welding work
surface.
3. The stir welding system of claim 1, comprising strips configured
to fit in the curved grooves while securing the tungsten-based
member to the backing plate and wherein the strips are generally
flush with the welding work surface.
4. The stir welding system of claim 1, wherein the backing plate
comprises liquid passages configured to cool or heat the
tungsten-based member and one or more workpieces.
5. The stir welding system of claim 1, wherein the backing plate
comprises gas passages configured to cool or heat the
tungsten-based member and one or more workpieces.
6. The stir welding system of claim 5, wherein the gas passages are
configured to flow a shielding gas.
7. The stir welding system of claim 1, wherein the tungsten-based
member comprises a plurality of sections disposed one after another
along a direction of the stir weld.
8. The stir welding system of claim 7, wherein the plurality of
sections comprises an initial pin tool contact section and a stir
welding section.
9. The stir welding system of claim 1, wherein the tungsten-based
member comprises tungsten that includes a dopant material, wherein
the dopant material comprises lithium, sodium, potassium, rubidium,
cesium, lanthanum oxide, yttrium oxide, cerium oxide, thorium
oxide, or a combination thereof.
10. A stir welding system, comprising: a backing plate, comprising
a cavity; a tungsten-based member disposed along the backing plate
and received by the cavity to define a generally flush welding work
surface including both the backing plate and the member, and the
tungsten-based member comprises curved grooves configured to secure
the member to the backing plate and the member further comprises a
plurality of sections positioned one after another along a
direction of a stir weld.
11. The stir welding system of claim 10, wherein the backing plate
comprises liquid passages configured to cool or heat the
tungsten-based member and one or more workpieces.
12. The stir welding system of claim 10, wherein the backing plate
comprises gas passages configured to cool or heat the
tungsten-based member and one or more workpieces.
13. The stir welding system of claim 12, wherein the gas passages
are configured to flow a shielding gas.
14. The stir welding system of claim 10, wherein the plurality of
sections comprises an initial pin tool contact section and a stir
welding section.
15. The stir welding system of claim 10, wherein the plurality of
sections and the cavity are configured to adjoin each other at an
end of each section.
16. The stir welding system of claim 10, wherein the tungsten-based
member comprises an arcuate surface opposite from the welding work
surface, wherein the welding work surface is generally flat.
17. A stir welding system, comprising: a backing plate comprising
liquid passages and gas passages, and further comprising a cavity;
and a tungsten-based member disposed along the backing plate and
received by the cavity, wherein the tungsten-based member defines a
generally flush welding work surface including both the backing
plate and the member, and wherein the member comprises curved
grooves configured to secure the member to the backing plate.
18. The stir welding system of claim 17, wherein the tungsten-based
member comprises an arcuate surface opposite from the welding work
surface, wherein the welding work surface is generally flat.
19. The stir welding system of claim 17, wherein the gas passages
are configured to flow a shielding gas.
20. The stir welding system of claim 17, comprising a pin tool
movable by a drive to create friction along one or more workpieces
disposed on the welding work surface, wherein the frictional
heating and mechanical stirring is configured to create a stir weld
along the one or more workpieces.
21. The stir welding system of claim 17, wherein the liquid
passages and gas passages are configured to cool or heat the
tungsten-based member and one or more workpieces.
Description
BACKGROUND
The invention relates generally to solid state welding technology,
and more particularly to friction stir welding.
Increasing the output and efficiency of turbo-machinery such as gas
turbine engines requires optimization of materials that balance
high temperature strength, creep and fatigue resistance, oxidation
and corrosion resistance, as well as structural stability, among
others. In many cases, the alloying content requirements of these
materials have dictated a powder processing approach to prevent
material segregation. When joining these, as well as many
conventionally cast materials, it is often advantageous to remain
below the melting temperature, thereby eliminating issues commonly
observed in traditional fusion welding processes, such as
solidification induced cracking and porosity, weld zone material
segregation, and the formation of a rapidly solidified cast
microstructure.
Solid state welding or joining processes have been developed as a
way of addressing these issues. One of the more successfully
employed techniques is friction stir welding, which can be used to
join similar or dissimilar metals and alloys, thermoplastics, or
other materials. The solid-state nature of this technique addresses
the above mentioned issues associated with other more conventional
joining techniques, enabling the joining of materials otherwise
considered difficult or impossible to weld.
In a typical friction stir welding system, a rotating, often
cylindrical, consumable or non-consumable pin tool may be plunged
into a rigidly clamped workpiece at a location containing a linear
or non-linear joint to be welded. Frictional heating locally
plasticizes the workpiece, enabling material transfer across the
joint interface through a forging and/or extrusion action about the
rotating pin tool. Ideally, workpiece temperatures remain below the
melting temperature of the material throughout the duration of the
weld. In many material systems, precise through-thickness control
of in-situ weld metal heating and cooling rates is also critical to
the quality of the weld. Improved control over in-situ pin tool and
workpiece temperatures can also prevent bonding between the
workpiece and the backplate, undesirable workpiece material
structure, and destruction of the backplate components.
BRIEF DESCRIPTION
A system, in certain embodiments, includes a backing plate, a
tungsten-based member disposed along the backing plate, wherein the
tungsten-based member defines a welding work surface, and the
tungsten-based member comprises curved grooves configured to secure
the tungsten-based member to the backing plate. Alternate suitably
high strength/high temperature materials can be substituted as the
welding work surface, in place of the tungsten based member. The
system also includes a drive. The system also includes a pin tool
movable by the drive to create friction along one or more
workpieces disposed on the welding work surface, wherein the
friction is configured to create a stir weld along the one or more
workpieces. The system, in some embodiments, also may include a
backing plate comprising liquid passages and gas passages and a
tungsten-based member disposed along the backing plate, wherein the
tungsten-based member defines a welding work surface. Alternate
suitably high strength/high temperature materials can be
substituted as the welding work surface, in place of the tungsten
based member.
DRAWINGS
These and other features, aspects, and advantages of the present
invention will become better understood when the following detailed
description is read with reference to the accompanying drawings in
which like characters represent like parts throughout the drawings,
wherein:
FIG. 1 is a block diagram of an embodiment of a friction stir
welding system;
FIG. 2 is a block diagram of an embodiment of a friction stir
welding system, wherein a pin tool is engaging workpieces;
FIG. 3 is a partial top view of an embodiment of a friction stir
welding system as shown in FIGS. 1 and 2;
FIG. 4 is a partial top perspective view of an embodiment of a
friction stir welding system as shown in FIGS. 1 and 2, with
certain components removed to enhance clarity;
FIG. 5 is a partial end view of an embodiment of a friction stir
welding system as shown in FIGS. 1 and 2;
FIG. 5A is a detailed view of curved grooves of a tungsten-based
member, as shown in FIG. 5; and
FIG. 6 is a partial top view of another embodiment of a friction
stir welding system.
DETAILED DESCRIPTION
One or more specific embodiments of the present invention will be
described below. In an effort to provide a concise description of
these embodiments, all features of an actual implementation may not
be described in the specification. It should be appreciated that in
the development of any such actual implementation, as in any
engineering or design project, numerous implementation-specific
decisions must be made to achieve the developers' specific goals,
such as compliance with system-related and business-related
constraints, which may vary from one implementation to another.
Moreover, it should be appreciated that such a development effort
might be complex and time consuming, but would nevertheless be a
routine undertaking of design, fabrication, and manufacture for
those of ordinary skill having the benefit of this disclosure.
When introducing elements of various embodiments of the present
invention, the articles "a," "an," "the," and "said" are intended
to mean that there are one or more of the elements. The terms
"comprising," "including," and "having" are intended to be
inclusive and mean that there may be additional elements other than
the listed elements. Any examples of operating parameters and/or
environmental conditions are not exclusive of other
parameters/conditions of the disclosed embodiments.
As discussed in detail below, various configurations of friction
stir welding systems may be employed to manage the temperature of
the workpieces, welding pin tool, and backing plates. An example of
the workpiece material to be welded is a titanium alloy, e.g., for
use in aerospace applications. The temperature of such workpieces
may exceed 1800 degrees Fahrenheit during a stir welding process.
In addition, the backing plate and workpiece surface may be
subjected to 10,000 to 20,000 pounds of force during the process.
Further, the systems below may be applicable to joining workpieces
using adiabatic heating in addition to stir welding. As discussed
below, such forces and temperatures may cause deformities in the
backing plates and cause the workpieces to bond to the backing
plate. In an embodiment, a member made of material that is harder
than surrounding materials in the backing plate may be utilized to
control the temperature of workpieces. Specifically, the
embodiments discussed below may employ a tungsten-based member
located on the backing plate along the weld axis to withstand the
high thermal and mechanical loads that occur along the weld joint.
The tungsten-based member may be placed in a cavity of the backing
plate and may be generally flush with the working surface of the
backing plate. The member, made of tungsten, or another suitable
thermally conductive material, may have cooling lines beneath it
for flowing gas and/or liquid to control the temperature of the
workpiece. Further, the stir welding system may include channels in
the backing plate or in other portions of the system to cool or
heat system components, thereby managing the temperature of the pin
tool and workpieces to produce an overall better weld. The channels
may utilize liquid and/or gas to manage the temperature of the
system and workpieces.
In another embodiment, a plurality of tungsten-based members may be
placed end to end along the weld axis. A sacrificial tungsten-based
member may be placed below the portion of the joint where the pin
tool is plunged into the workpieces. This initial contact
tungsten-based member is exposed to extreme temperatures and
stresses, relative to the rest of the weld axis, and therefore may
be replaced more frequently than tungsten-based members located
along the remaining portion of the weld axis. As described herein,
the weld axis is the line along which the joint between two
workpieces is located. Moreover, additional tungsten-based members
may also be located at the end of a first "main section"
tungsten-based member, to allow for longer stir weld joints. By
implementing these embodiments, workpiece heating rates, in situ
workpiece temperature profile, and high post-weld workpiece cooling
rates may be managed to result in a weld joint of improved utility
to the overall weld application design. Further, the techniques may
reduce or eliminate bonding between the workpiece and the
backplate, undesirable workpiece material structure, and
destruction of the backplate components.
FIG. 1 is a block diagram illustrating an embodiment of friction
stir welding system 10. In the embodiment, tungsten-based member 12
is coupled to backing plate 14. As depicted, drive unit 16 powers
the movement of pin tool 18. In an embodiment, the pin tool 18 may
be rotated at speeds between about 50 RPM and about 2000 RPM during
the stir welding process to create a stir weld joint between
workpieces 20. As discussed in detail below, tungsten-based member
12 may be mounted directly below a desired weld joint location,
thereby providing greater resistance to heat, wear, and stresses
associated with friction stir welding. Tungsten-based member 12 may
include a doped or undoped tungsten, which may or may not be
alloyed with alternate elements. The dopant material may include at
least one material of lithium, sodium, potassium, rubidium, cesium,
lanthanum oxide, yttrium oxide, cerium oxide, or thorium oxide. For
example, member 12 may comprise doped or undoped, alloyed or
unalloyed tungsten that includes a dopant material and/or alloyed
or unalloyed tungsten. An example of one such tungsten-based member
may be found in U.S. Pat. No. 7,337,940, filed on Apr. 24, 2006,
which is herein incorporated by reference in its entirety for all
purposes. In addition, U.S. patent application Ser. No. 11/554,751
is herein incorporated by reference in its entirety for all
purposes. In another embodiment, an alternate suitably high
temperature/high strength material can be used in place of the
tungsten-based member 12. Some examples of materials that may be
used in place of the tungsten material may include Mar-M247, IN100,
ALLVAC 718PLUS, and for lower temperature applications, tool steels
and stainless steels.
In addition, the high strength material may be about 10%-50%
stronger than the material that surrounds member 12.
As depicted, the rotating pin tool 18 may be plunged into clamped
workpieces 20 at a location containing a joint to be welded. The
workpieces 20 may be clamped into place on the steel backing plate
14 during welding. The rotating pin tool 18 can be traversed along
the joint to be welded, held in place as the workpieces 20 are fed
past the tool 18, or any combination of the two. As the weld
progresses, the workpiece material within the joint vicinity
becomes a plasticized (non-liquid) metal, metal alloy or other
material. As the tool 18 works across the joint, workpiece material
from the joint transfers across the joint interface, co-mingling to
form a strong cohesive bond between the workpiece components
through a localized solid-state forging and/or extrusion
action.
In the embodiment, workpiece surface 22 is generally flat so as to
ensure an optimal surface between tungsten-based member 12 and
workpieces 20. The flat workpiece surface 22 is configured to
optimize temperature distribution between various components of the
stir welding system 10 and workpieces 20. The temperature of
workpieces 20 may be managed in part by gas channels 24 located
inside backing plate 14. Gas channels 24 may be used to circulate a
gas, inert or otherwise, such as argon, to assist in cooling and/or
heating workpieces 20, tungsten-based member 12 and/or backing
plate 14. As appreciated, gas channels 24 may also provide inert
gas shielding specifically but not limited to the underside of the
workpiece during the stir welding process, thereby substantially
reducing oxidation and degradation of the welding joint. In the
embodiment, backing plate 14 also includes liquid channels 26,
which may be used to cool and/or heat the backing plate 14,
tungsten-based member 12, and/or workpieces 20. Gas channels 24 are
connected by gas lines 28 to gas circulation system 30, which may
be used to control the flow rate and the temperature of a gas
circulating through backing plate 14. Liquid channels 26 are
connected via lines 32 to liquid heat exchanger system 34, which
may be used to regulate the flow rate and the temperatures of
backing plate 14, tungsten-based member 12 and/or workpieces 20. In
other embodiments, either liquid channels 26 or gas channels 24 may
be used alone to manage the temperature of stir welding system 10.
Further, the configuration, size, geometry, and location of liquid
channels 26 and/or gas channels 24 may be altered to optimize
thermal performance, simplify manufacturing, or meet other
application requirements.
In the embodiment, the tool temperature control system 36 is
coupled to pin tool drive unit 16 in order to monitor and regulate
the temperature of pin tool 18. Temperature control system 36 may
use gas, liquid, or other suitable heat exchange/transfer elements
to control the temperature of pin tool 18 as it creates a stir weld
joint. Welding control system 38 may be used to monitor the
movement and speed of pin tool 18, tool temperature control system
36, gas circulation system 30, and liquid heat exchanger system 34.
Welding control system 38 may include one or more computers that
may be used to perform an algorithm or other software programs to
coordinate and regulate the operation and temperature of friction
stir welding system 10 and its components. Further, monitoring
system 40 may be connected to control system 38, thereby enabling
temperature monitoring of various components of friction stir
welding system 10. As depicted, monitoring system 40 has sensors,
such as thermocouples, located in pin tool drive 16 and
tungsten-based member 12.
In a particular embodiment, the liquid channels 26 and gas channels
24 may be used to pre-heat, heat, and/or post-weld heat a weld
affected region. The heat may be used to decrease stress on the
workpieces 20 and/or control the post-weld cooling rate within the
weld affected region, and thus provide a desired microstructure or
provide other benefits such as improved tool performance, and
optimized weld properties. In an alternative embodiment, heating
may also be provided by multiple resistive heaters. Other examples
of heating methods may include passing a fluid as a temperature
control media, microwave heating, laser heating, ultrasonic heating
and induction heating. Using a fluid, such as a gas or liquid, to
control the weld affected region enables a low maintenance and
effective method for temperature control. For example, an external
tank may store and cool a liquid, that features desirable
thermodynamic properties, which may be circulated to control a
temperature of components within friction stir welding system 10.
In another embodiment, the liquid channels 26 and gas channels 24
may be used to cool the weld affected zone in order to extract heat
from the weld. Water or any suitable cooling fluid or gas may flow
through the liquid channels 26 and gas channels 24 of the backing
plate 14.
As shown in the FIG. 1, workpieces 20 are located above flat
workpiece surface 22 prior to positioning for the stir welding
process. In the embodiment, workpieces 20 may be composed of
similar or dissimilar suitably high strength materials such as
Ti-base, Ni-base, and Fe-base alloys, or other high performance
material compositions, such as those that may be used for
components of turbine engines. As previously discussed, stir
welding of high strength materials may lead to degradation of
certain properties in the materials, which may be avoided or
reduced by managing the temperature of workpieces 20 and certain
components of friction stir welding system 10 using the embodiments
discussed herein. Therefore, many configurations of friction stir
welding system 10 may be envisioned, featuring inert gases,
liquids, and/or other suitable techniques for heating or cooling,
controlled by a computer or other suitable devices.
FIG. 2 is a diagrammatic illustration of an embodiment of friction
stir welding system 10, wherein workpieces 20 and pin tool 18 are
positioned to perform a stir weld. In the embodiment, workpieces 20
are placed together near the middle of tungsten-based member 12 and
directly beneath pin tool 18. As depicted, an operator may
configure the control system 38 to have the drive unit 16 and pin
tool 18 moved downward, thereby plunging pin tool 18 into weld
joint 40 as pin tool 18 rotates at the desired speed. As
appreciated, the rotation of pin tool 18 directly against
workpieces 20 creates significant friction and heat, thereby
enabling a solid state bond to form as indicated by weld joint 40
between the two workpieces 20. In the embodiment, the temperature
of workpieces 20, pin tool 18, tungsten-based member 12 and other
components may be monitored and regulated, thereby ensuring that
the structural irregularities and degradation of workpieces 20 are
minimized. In particular, the composition of tungsten-based member
12 and its location along the weld axis, beneath weld joint 40,
help increase the overall quality of the stir weld. In an
embodiment, the materials chosen for pin tool 18 and tungsten-based
member 12 may be the same and are particularly useful in
maintaining and controlling the temperature of workpieces 20 during
the stir weld process.
FIG. 3 is an illustration of a top view of an embodiment of
friction stir welding system 10 featuring gas channels 24 and
liquid channels 26. In the embodiment, gas channels 24 are
connected to gas circulation system 30 via gas line 28. Gas
channels 24 circulate a gas, inert or otherwise, through backing
plate 14 and release the heated or cooled gas through gas outlets
holes 42, which may be located in the top surface of strips 44. In
the embodiment, gas outlet holes 42 are distributed throughout stir
welding system 10 to control the temperature of the components and
the workpieces. Gas released from gas outlet holes 42 may also be
used to shield the weld joint during the weld process, thereby
protecting the joint from impurities and/or oxidation. In the
embodiment, strips 44 are used to secure tungsten-based member 12
in place, thereby ensuring that tungsten-based member 12 is not
moved by forces exerted during the stir welding process. Strips 44
may be made of a steel alloy or other suitable material that is
able to hold down tungsten-based member 12 while possessing the
desired weight and thermal properties.
In the embodiment, gas channels 24 are located beneath strips 44
and backing plate 14. Gas outlet holes 42 may be located in any
suitable location in the stir welding system 10 to achieve the
desired thermal control and shielding that may be utilized by the
stir welding system 10. As depicted, liquid exchanger system 34 is
connected via lines 32 to liquid channels 26, which may be located
in any suitable location in the backing plate 14 or in other
components of the friction stir welding system 10. Liquid channels
26 run underneath tungsten-based member 12 to maximize the effect
of the liquid temperature control on the workpieces.
As shown, initial contact section 46 is located at one end of
backing plate 14. Initial contact section 46 may be located
underneath the section of the workpiece where the pin tool drive
unit 16 may be initially plunged into the workpiece joint. The pin
tool 18 may then move down the joint, along the weld axis, with
reduced pressures and force on the tungsten-based member and other
components located in main section 47. In certain embodiments, the
process of plunging the pin tool into the workpiece creates
significant forces and wear and tear on the components located at
the point of initial contact with the workpieces. The components
included in the initial contact section 46 may be subject to more
extreme forces, wear and tear, which may result in more frequent
maintenance and/or replacement than the components located in main
section 47. Also included in initial contact section 46 are
tungsten-based member 48, strips 50 and backing plate 52. In the
figure, strips 44 and 50 may be held down by screws 54 which may be
screwed to countersunk holes in the strips, thereby ensuring an
optimal flat surface for the workpieces.
The components of initial contact section 46 may be composed of
similar materials to the components of main section 47 or may be
composed of alternate, potentially less expensive materials, due to
the fact that initial contact section 46 may be replaced more
frequently. For example, after performing five to ten stir weld
processes, tungsten-based member 48 and strips 50 may be deformed
or their working surface may not be as smooth as that of components
of main section 47. Moreover, the deformed portions of initial
contact section 46 may cause degradation of the materials of the
workpieces 20 and weld joint 40. Therefore, it may be desirable to
replace initial contact section 46 or its components after five to
ten uses to ensure high quality stir welds. Further, main section
47 components may not experience the extreme forces that initial
contact section 46 is subjected to, thereby preserving the
integrity the components of main section 47. For example, main
section 47 may utilize the same components without maintenance or
replacement for 300 to 500 or more stir welding operations.
FIG. 4 is a perspective view of an embodiment of friction stir
welding system 10. In the diagram, initial contact section 46 is
located at one end of the friction stir welding system 10 adjacent
to main section 47. Tungsten-based member 48 is located in initial
contact section 46 and abuts an end of tungsten-based member 12. In
the embodiment, gas outlet holes 42 are located axially along
strips 44, which are located on either side of tungsten-based
member 12. Further, backing plate 14 may be mounted on another
member, such as base 56, which may be composed of any suitable
material such as a steel alloy. In an embodiment, base 56 may also
include liquid and/or gas channels to route cooling and heating
materials to the working surface of backing plate 14. As depicted,
backing plate 14 includes gas inlet hole 58 as well as liquid flow
holes 60, which may be located on the side of backing plate 14. The
components of initial contact section 46 and the components of main
section 47 are held in place by end sections 62. End section 62 may
be coupled to backing plate 52 and backing plate 14 by screws 64.
In the embodiment, tungsten-based member 48 may also be held in
place by screw adjustment 66. As shown, the used of certain
materials, such as tungsten-based members 12 and 48, as well as gas
and liquid temperature control channels will enable temperature
management of workpieces 20 and will produce an optimal workpiece
surface for stir welding.
FIG. 5 shows an end-view of an embodiment of friction stir welding
system 10. The embodiment includes pin tool drive unit 16, pin tool
18, workpieces 20, and other components of the stir welding system.
In the embodiment, workpieces 20 are placed on generally flat
workpiece surface 22, which creates an optimal surface for heat
transfer and force distribution during the stir welding process. In
the illustration, a cross-section of tungsten-based member 12 and
strips 44 is shown. Tungsten-based member 12 is recessed in the
cavity of backing plate 14, and is captured between strips 44 and
the backing plate 14. In other words, strips 44 may be used to
secure tungsten-based member 12 into place within the recess. In
the exemplary embodiment, the tungsten based member 12 has a flat
top surface 22, an arcuate bottom surface 67 (e.g.,
semi-cylindrical), and a pair of grooves 68 recessed along opposite
sides of the flat top surface 22. The arcuate bottom surface 67 may
improve centering, improve force distribution, and reduce stresses
associated with friction stir welding. The illustrated grooves 68
also may have a curved geometry to optimize force distribution
during the stir welding process. For example, the corner of strips
44 that interface the grooves 68 of tungsten-based member 12 may be
rounded so as to reduce the possibility of structural degradation
or movement of the tungsten-based member during the stir welding
process. An embodiment of tungsten-based member 12 may include
curved grooves, featuring the curved or rounded corners as
illustrated in the diagram, wherein the strips 44 secure the
tungsten-based member in place against the backing plate 14. The
arrangement of strips 44 and tungsten-based member 12 produces a
generally flat workpiece surface 22, which provides improved heat
distribution and management during the stir welding process. FIG.
5A is a detailed view of the curved grooves 68 of tungsten-based
member 12, as shown in FIG. 5.
FIG. 6 is an illustration of another embodiment of friction stir
welding system 10, including initial contact section 46, main
section 47 and modular section 70. In the embodiment, modular
section 70 may be placed at an end of main section 47, thereby
enabling a longer stir weld joint than allowed by previous
embodiments. As depicted, modular section 70 includes backing plate
72, tungsten-based member 74, and strips 76. In the embodiment, the
components of modular section 70 may be made of the same materials
as main section 47, or may be duplicates of the components of main
section 47. For example, tungsten-based member 74 may be made of
the same material as tungsten-based members 12 and 48. Similarly,
strips 50, 44, and 76 may be composed of a steel alloy. During an
exemplary stir welding operation, the pin tool 18 may be plunged
into a workpiece 20 while the pin tool is located above
tungsten-based member 48. After becoming fully plunged into the
workpiece 20, the pin tool 18 may be moved along tungsten-based
member 12, across the weld axis, and may continue over
tungsten-based member 74 of modular section 70 in the present
embodiment. The illustrated arrangement enables longer stir welds
than may be allowed in other embodiments of the stir welding system
10. In some embodiments, stir welding system 10 may also feature
liquid and/or gas temperature control channels in initial contact
section 46, main section 47, and modular section 70 in order to
manipulate the temperature of system components and workpieces. In
other embodiments, multiple modular sections 70 can be employed to
extend the weld length indefinitely.
It should be understood that the temperature management techniques,
materials used, and system configurations described above may be
used in friction stir welding systems of different configurations
as well. For example, the tungsten-based members may be used as
"shoulders," located on the inside corners of backing plates of a
T-joint stir welding system. Further, such a system may employ gas
and/or liquid to manage the temperature of the workpieces and
system components. In yet another example, the workpiece surface 22
may be curvilinear to accommodate non-linear and/or contoured
joints.
The various embodiments of a system for controlling microstructure
and properties of workpiece materials via temperature management
described above illustrates a way to improve or preserve material
properties including but not limited to yield strength, tensile
strength, ductility, impact toughness, fracture toughness, fatigue
crack growth resistance, low cycle fatigue resistance, high cycle
fatigue resistance, and superplastic formability of a friction weld
and surrounding regions.
While only certain features of the invention have been illustrated
and described herein, many modifications and changes will occur to
those skilled in the art. It is, therefore, to be understood that
the appended claims are intended to cover all such modifications
and changes that fall within the true spirit of the invention.
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